Turbine rotor with means for preventing air leaks through outward end of spacer

ABSTRACT

A turbine rotor provided with a sealing member for preventing air leaks through a gap between the under side surface of a projection extending from one of discs of the rotor and the upper side surface of a outward end portion of the spacer interposed between the discs. The spacer is formed with an annular groove on the upper side surface of the outward end portion for receiving a sealing wire in its entirety. The sealing wire has its outer portion forced against the underside surface of the projection by centrifugal forces while its inner portion remains inside the groove during turbine operation, to thereby seal the gap to prevent leaks of air therethrough.

BACKGROUND OF THE INVENTION

This invention relates to turbine rotors of gas turbines, steamturbines, etc., and, more particularly, to a turbine rotor comprising aplurality of shafts and turbine discs each with including a bladesecured to an outer periphery of a turbine wheel, a spacer mountedbetween the two adjacent discs, and with the rotor being provided withmeans for preventing a leakage of air flowing through the interior ofthe rotor for cooling the through an outer end of the spacer.

Generally, a rotor formed by combining a plurality of discs and shaftsis constructed such that discs and shafts are stacked in a superposedrelation and secured to one another by bolts so as to form the rotor.

However, a rotor of the aforementioned type suffers the disadvantagethat air leaks through the outer end of the spacer in large amount aswill be more fully understood from the following description of acooling air system of a prior art rotor shown in FIG. 1.

More particularly, as shown in FIG. 1, a rotor includes at least firstand second stage a wheels 1 and 3, a plurality of blades 4 and 5respectively secured to outer peripheries of the wheels 1, 3 to formdiscs generally designated by the reference numerals 1a and 3a, a spacer2 being interposed between the two discs 1a, 3a and shafts S1 and S2,stacked in superposed relation, secured to the discs 1a, 3a. Acombustion gas flowing in a direction incidated by an arrow A impingeson the blades 4 and 5 to rotate the rotor. The wheels 1, 3, in the formof discs coaxial with the shafts S1, S2, are respectively formed withair passages 1b and 3b in central portions thereof. In this case, air 9for cooling the blades 4 and 5 is led to the interior of the rotorthrough inlet ports 10 and flows through the air passages 3b in thecentral portion of the rotor before reaching an inner space 21 of thespacer 2 between the first stage wheel 1 and the second stage wheel 3.The spacer 2 is formed with a plurality of slits 8 at a surface thereofcontacting the first stage wheel 1 for maintaining communication betweenthe inner space 21 and an air sump 6 adjacent the outer periphery of therotor. Thus, the air 9 for cooling the blades 4 and 5 flows through achannel constitutetd by the inlet ports 10, the central portion of therotor, i.e. air passages 1b and 3b, inner space 21 of the spacer 2,slits 8 and cooling air sump 6.

As shown in FIG. 2, the cooling air 9 entering the cooling air sump 6,after flowing through the slits 8, is introduced into a bottom groove 7between the first stage wheel 1 and the first stage blade 4 and thenflows into radially extending blade cooling ducts 12 in the first stageblade 4 to cool same, before being vented through a top portion 41 ofthe blade 4.

To enable the cooling air 9 to attain the end of effectively cooling thefirst stage blade 4, the cooling air 9 only has to be led from thecooling air sump 6 to the bottom groove 7 without any air leaks. To thisend, attempts have been made to provide the blade 4 with a projection 42which is located at a lower portion of the blade 4 and extends towardthe center of the rotor in such a manner that it overlaps the outerperiphery of the spacer 2 to prevent air leaks through the outward endportion of the spacer 2, as viewed in a peripheral direction of thespacer 2. However it is impossible to bring the first stage blade 4 intointimate contact with the spacer 2 during operation to eliminate a gap11 between the blade 4 and spacer 2 since it is necessary to provide aclearance between the projection 42 of the first stage blade 4 and thespacer 2 to avoid impinging of the projection 42 against the outerperipher of the spacer 2 which might otherwise occur due to anaccumulation of allowed tolerances of these parts when they areseparately fabricated. The provision of the clearance is also necessaryin view of deformation of the first stage wheel 1 and the spacer 2 whichwould occur during operation due to centrifugal forces and thermalstresses.

As shown in FIG. 3, length 11' of the gap 11, initially 0.24, becomeslonger by 0.05 mm during operation because the first stage wheel 1undergoes deformation in larger amount than the spacer 2 due to thecentrifugal forces of the first stage blade 4. Thus, the gap 11 has alength of 0.29 during operation. In FIG. 3, the line 13 depicts a risein rpm and a line 14 depicts a rise in a load. As apparent from FIG. 3,the length 11' of the gap 11 increases as the rpm rises and continues toincrease even after the rpm has become constant, until the load becomessubstantially constant, and thereafer the length 11' becomes flat.

As shown most clearly in FIG. 4, leaks 17, in kilograms per second, aresubstantially proportional to the length 11', and the leaks are largeeven if the gap 11 is small since the spacer 2 has a large diameter atits outer periphery and the cooling air 9 in the cooling air sump 6 is ahigh pressure. The leaks 17 represent about 40% of the air cooling thefirst stage blade 4 and about 0.5% of the main gas flowing in stream.

In FIG. 5, the ordinate represents a percentage reduction in thermalefficiency and as can be seen from FIG. 5, the thermal efficiency showsa reduction of 0.25% which represents a great loss.

Thus, the prior art suffers the disadvantage that the leaks through thegap between the projection 42 of the first stage blade 4 and the spacer2 cause a reduction in thermal efficiency. This also gives rise to theproblem that the gap 11 shows a change in size due to deformation of thewheel 1, 3 and spacer 2 during rotor operation and the cooling air hasnonstatic stability.

SUMMARY OF THE INVENTION

This invention has been developed for the purpose of obviating theaforesaid problems of the prior art with regard to the gap between theblade and the spacer. Accordingly the invention has as its object theprovision of a turbine rotor with means for preventing air leaks througha outward end of the spacer capable of avoiding the cooling air becomingnonstatic due to a change in the gap size by reducing leaks of thecooling air through the outward end of the spacer, to thereby increasethe efficiency with which the blades are cooled and improve the thermalefficiency of the rotor.

To accomplish the aforesaid object, the invention provides means forsealing the gap between the discs constituted by wheels having bladessecured thereto and the spacer interposed between the discs bycentreifugal forces during rotor operation.

The invention can achieve the effect of preventing leaks of the coolingair through the forward end of the spacer by virtue of the sealing meansduring rotor operation, thereby improving the thermal efficiency of therotor.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a cross-sectional view of the construction of a rotor of theprior art;

FIG. 2 is a fragmentary cross-sectional detail view of, on an enlargedscale, the rotor shown in FIG. 1;

FIG. 3 is a graphical illustration of a relationship of a gap lengthwith respect to elapsed time following a start-up of a turbine employingthe rotor of FIG. 1;

FIG. 4 is a graphical illustration of a relationship of gap length toair leakage;

FIG. 5 is a graphical illustration of thermal efficiency caused by airleakage;

FIG. 6 is a cross-sectional view of portions of a rotor comprising oneembodiment of the present invention;

FIG. 7 is a schematic plan view of a sealing wire of rotor in FIG. 6;and

FIGS. 8a and 8b are cross-sectional views of a modification of thesealing wire shown of FIG. 7.

DETAILED DESCRIPTION

Referring now to the drawings wherein like reference numerals are usedthroughout the various views to designate like parts and, moreparticularly, to FIG. 6, according to this figure, a rotor comprises afirst stage wheel 1 and a second stage wheel 3, and a first stage blade4 and a second stage 5 respectively placed on outer peripheral portionof the wheels 1, 3 to form discs 1a, 3a. A spacer 2 is mounted betweenthe discs 1a, 3a, so that the discs 1a, 3a and the spacer 2 are combinedwith shafts S1, S2 (FIG. 1) to form the rotor. The rotor is constructedsuch that a current of air is passed through its interior thereof tocool the blades 4, 5. A seal 16 is mounted between the disc 1a and thespacer 2 to prevent leakage of air through the outward or outerperipheral end of the spacer 2.

The first stage blade 4 is formed with a projection 42 extending towardthe spacer 2 in such a manner that an inner side surface thereof islocated in a superposed relationship with respect to the outer sidesurface of the spacer 2. The spacer 2 is formed, in a portion thereof,located below the projection 42, with a sealing groove 15 which extendsabout the entire periphery of the spacer 2. The groove 15 is locatedimmediately below or directly inwardly of the projection 42 of the blade4 and has a width which is smaller than the length of the projection 42.The groove 15 has a depth which is equal to the width thereof and shouldbe over ten times a gap l between the blade 4 and the spacer 2. The gapl may become wider when the rotor operates as described above inconnection with FIG. 3, so that if the groove 15 is too shallow ornarrow, a wire 16, which serves as a sealing member might be dislodgedtherefrom or caught between the spacer 2 and projection 42 and causetrouble. Thus, the groove 15 preferably has a substantial depth, and itis considered likely that if the depth of the groove 15 is over tentimes as great as the gap l there is almost no risk of developingtrouble.

The sealing wire 16, of the same diameter as the width of the groove 15,is placed in the groove 15 as a sealing member to be snugly fittedtherein. In actual practice, the sealing wire 16 may have a width whichis slightly smaller than the width of the groove 15 so as to enable thewire 16 to be shifted by centrifugal forces outwardly or upwardly inFIG. 6 in the groove 15 when the rotor rotates thereby intentionallybringing the wire 16 into pressing engagement with the inner sidesurface or lower side surface of the projection 42 of the blade 4.

The sealing wire 16 extends about the entire outer circumference of therotor along the outer side surface of the spacer 2. As shown in FIG. 7the sealing wire 16 is split into, for example, for segments. If thesealing wire 16 were in one piece, it would be difficult for the wire 16to be shifted outwardly from the groove 15 when the spacer 2 is forcedto move outwardly by centrifugal forces. However, by splitting the wire16 into a plurality of segments, it is possible for the wire 16 to bereadily deformed radially outwardly as indicated by an arrow B so thatthe wire segment would be deformed as shown dash-and-dot lines.

The sealing wire 16 may be embedded in the groove 15 of the spacer 2when the parts are stacked to form the rotor, and the spacer 2 may bestacked on the first stage wheel 1 in a superposed relation.

As shown in FIG. 8a, when the parts of the rotor are assembled, theouter side surface of the spacer 2 and the outermost peripheral surfaceof the sealing wire 16 in the groove 15 are flush with each other. Asthe rotor rotates, the sealing wire 16 is urged to move outwardly of thegroove 15 by centrifugal forces or by a force acting thereon in thedirection of the arrow B in FIGS. 6-8 thereby resulting in the sealingwire 16 being shifted in the direction of the arrow B into abuttingengagement with the projection 42 of the spacer 2. An increase in thenumber of revolutions of the rotor causes the centrifugal forces of thesealing wire 16 to overcome the resilience thereof, with a result beingthat the sealing wire 16 undergoes deformation and the diameter thereof,as measured at its outermost periphery, becomes equal to the innerdiameter, that is, the diameter of the peripheral surface constituted bythe inner side surface of the projection 42 of the blade 4. Thus, thesealing wire 16 is brought into intimate contact with the blade 4 asshown in FIG. 8b on the outer peripheral surface of the wire 16 therebyenabling the clearance 11 to be perfectly closed by the sealing wire 16and eliminating leaks of the cooling air 9 through the gap 11. Even ifthe gap 11 changes its size as a result of deformation of the wheel 1 orspacer 2 due to rotor operation, the sealing wire 16 is capable ofperforming the sealing function and no leaks of the cooling air 9 occur.

The sealing wire 16 is split into a plurality of segments along itsextension, so that the wire 16 can be readily deformed by thecentrifugal forces and pressed against the projection 42 of the spacer 2to be brought into intimate contact therewith, to positively perform asealing function. If the wire 16 were split into segments, a gap d (seeFIG. 7) may be formed between the adjacent wire segments; however, thegap d is very small and air leakage therethrough is insignificant so asnot to cause any problem in actual practice.

While no gaps are formed in a one piece sealing wire 16, a one piecesealing wire 16 would require centrifugal forces of high intensity toovercome the resilience thereof.

Any material may be used for forming the sealing wire 16 so long as itenables the wire to perform a sealing fuction. For example, a piano wireor a wire of stainless steel may be used; however, different materialsmay be used for forming the sealing wire 16 depending on the temperatureat which the wire is used; namely, or the conditions under which it isused intensity of centrifugal forces, leaks without means forprevention, one piece or segmental form of sealing wire, etc. It is notso much the material of the sealing wire 16 as the thickness or diameterthereof that is important in defining the ability of the sealing wire 16to perform the sealing function.

The sealing member in not limited to a wire, and it is sufficient forany known material to be used so long as the sealing membersatisfactorily perform the intended sealing function.

From the foregoing description, it will be appreciated that the rotoraccording to the invention is provided with means for preventing leaksof cooling air through a forward end of the spacer or through a gapbetween the disk formed by fixing the blade to the wheel and the spacerwith such leak preventing means comprising a sealing member capable ofproviding a seal to the gap by centreifugal forces when the rotorrotates. Thus, leaks of air through the gap can be positively preventedand all the cooling air in the interior of the rotor can be effectivelyused for cooling the blades with high efficiency. The sealing member hasenough elasticity to cope with any change in the size of the gap whichmight be caused by deformation of the wheel and the spacer during rotoroperation, to say nothing of being able to positively close the gap asit originally existed. This eliminates the occurrence of nonstaticstability of the cooling air which might otherwise be caused by a changein the gap, thereby enabling cooling effects to be positively achievedand allowing prevention of leaks of the cooling air to be effected, andis conducive to an improvement in thermal efficiency and in rotorefficiency.

What is claimed is:
 1. A rotor comprising:a plurality of turbine discseach having a blade secured to an outer periphery of a turbine wheel; aspacer means mounted between two adjacent discs, said turbine discs,said spacer means and turbine shafts being assembled to form a turbinerotor; and means for preventing a leakage of air through an outer end ofsaid spacer means of air flowing through an interior of said rotor tocool said blades, said means for preventing includes an annularprojection formed on an axial end surface of each of said discs, saidannular projecting extending axially toward said spacer means in such amanner that an inner annular surface of said annular projection islocated in a superposed relationship to an outer cylindrical surface ofsaid spacer means adjacent thereto, a circumferential groove formed insaid outer cylindrical surface of said spacer means facing said innerannular surface of said annular projection, and a sealing means mountedin said circumferential groove for sealing a gap between said outercylindrical surface of said spacer means and said inner annular surfaceof said annular projection under an action of centrifugal forces duringan operation of said rotor.
 2. A rotor as claimed in claim 1, whereinsaid sealing means includes a wire.
 3. A rotor as claimed in one ofclaims 1 or 2, wherein said sealing means is divided into a plurality ofsections and arranged about an outer periphery of said spacer means.